These results revealed that ageing wines in barrels made
by the traditional process resulted in wines with higher
concentrations of compounds produced by heating/toasting,
particularly furan compounds (furfural, 5-hydroxymethyl-furfural,
5-methyl-furfural), volatile phenols (guaiacol, 4-methyl-guaiacol,
isoeugenol, and allylsyringol), aromatic aldehydes (vanillin and
syringaldehyde), and maltol.

In contrast, wines aged in barrels heated by immersion had higher cis-whisky-lactone content.

Conclusions

Analyses of the volatile compounds in the wines confirmed that the main differences between the two processes concerned the concentrations of toasting compounds produced by heat/toasting: furan compounds, volatile phenols, and aromatic aldehydes. Wines aged in barrels made by the traditional process had higher concentrations of these compounds. On an olfactory level, wines aged in barrels heated by immersion exhibited less intense “oaky,” “toasty” and, to a lesser extent, “sawdust” aromas. Tasters also found these wines “fruitier.”

Analysis confirmed that the main differences between the two processes concerned the concentrations of toasting compounds. As we shown previously, the production of toasting compounds is an improbable process during the preheating stage (prior to bending) because of low temperature irrespective for fire or water process. That is why the possible explanation of difference consists in the different moisture content, which was higher for water immersion. The evaporation of additional water in the latter case decreases the quantity of calories transmitted to wood during toasting. This “loss of energy” reduces the degree of degradation of wood hemicelluloses and lignin and the production of respectively furan and pyran compounds and aromatic aldehydes and volatile phenols.

Analysis of these results revealed that the main differences concerned the olfactory descriptors. The “toasty” and “oaky” descriptors were significantly more intense when the raised barrel was preheated over a fire compared to heating by immersion. The other marked difference was that the intensity of the “fruity” descriptor was significantly higher following preheating by immersion.

Differences with a lower confidence level were observed for the “sawdust” and “acidity” descriptors, with slightly higher intensity for “sawdust” after traditional heating.

In contrast, the “acidity” descriptor was also apparently significantly more intense following preheating by immersion in a certain number of sensory analyses. Thus, on the basis of the findings presented in this article, it was not possible to draw any systematic conclusion concerning the difference in intensity of this descriptor, as the results depended on the type of “wine matrix” and the length of ageing time, rather than the bending process used.

There was no significant difference between the intensity of the other descriptors, especially those describing flavors.

Chemical analysis

Table IV shows the Student’s T-test results for paired
samples (preheating by immersion compared to fire). They
include the main differences of concentration of each
compound between wine aged in traditional fire-bent barrel
and paired wine which was aged in barrel preheated in water
before bending. Thus the values of differences could be
positive and negative. A positive difference indicates
that a higher amount of chemicals is found from the
traditional process, whereas a negative difference from
water immersion before bending.

Table IV includes the standard deviations of differences
between samples and values of paired samples T- test in
order to check whether distribution of differences is
different from 0. The low T-test p values means that the
difference is systematic across all pairs. Such values
are presented in bold characters in Table IV.